Various aspects of research in thyroid function and iodine metabolism are under investigation as follows: 1. Purification of thyroid peroxidase and determination of its chemical and physical characteristics; 2. Determination of the role of thyroid peroxidase in iodination and in thyroxine biosynthesis; 3. Elucidation of the mechanism of iodination of thyroglobulin and of the mechanism of iodothyronine biosynthesis; 4. Elucidation of the mechanism of action of the clinically used antithyroid drugs; 5. Studies of the changes in iodine metabolism and in thyroid function that accompany mild and severe iodine deficiency; 6. Assay of thyroid peroxidase in normal and abnormal human thyroid tissue; 7. Measurement of serum T4 and T3 in Rana catesbiana tadpoles at various stages of metamorphosis.